This invention relates to high voltage motor starters and more particularly, to a three-high high voltage motor starter enclosure including starter cells having compartments isolated from one another, mechanical and electrical interlocks to minimize electrical hazards, and front accessibility to all components and wiring to facilitate quick and easy inspection or component replacement.
Larger motors are frequently applied today to drive various machines and pumps to improve plant efficiency. For horsepower above 200, the overall cost of installation favors 2,000 to 5,000 volt motors. These types of motors require high voltage motor starters having electromagnetically operated air break contactors suitable for repeatedly switching polyphase circuits carrying large alternating currents at moderately high voltages and for interrupting such circuits under full load conditions even when the available short-circuit capacity (Three Phase Symmetrical) of the circuits is as high as 50 MVA, unfused, and up to a maximum of 350 MVA, fused.
Although high voltage air break contactors have been successfully designed as illustrated in U.S. Pat. No. 3,403,239 issued to Schramm et al on Sept. 24, 1968, the high voltage motor starter enclosures lagged far behind in providing accessibility to all of the components mounted within the enclosure. Prior art enclosures also has few mechanical and electrical interlocks to minimize electrical hazards. Recently, there has been a general recognition that the high voltage motor starter enclosures should include more than one starter cell and as many as three full voltage, non-reversing, squirrel cage starters or room to mount other motor starter configurations within a single enclosure. Furthermore, prior art starters lacked starter cell compartments which were isolated from one another such as line and load compartments. Also, the prior art enclosures seldom provided a means for withdrawing the contactor from both line and load connections with shutters that close over line and load connections to isolate the line and bus compartments from the high voltage contactor compartment while providing simple mechanical interlocks that operate separately from the drawout handle so that even if the mechanical interlocks usually associated with the drawout handle are defeated, the contactor cannot be racked into an energized position when the door of the high voltage compartment is open.
One further disadvantage of the prior art high voltage motor starter enclosures was the inaccessibility to the power and control transformer fuses, coils, relays, current transformers, and other electrical components located in the various compartments of each cell when the enclosures were up against a wall or in line with other switch gear cabinets.
Moreover, many of the prior art enclosures with only mechanical interlocks on their drawout handle included few electrical disconnects in the secondary of the control transformer to assure the safety of authorized service personnel.